The technology for employing two pulses for rocket motors adopts a system in which two propellants are placed in a single pressure vessel separated by a barrier membrane, and the second propellant is protected from heat of first propellant burning by the barrier membrane so that the second pulse is not activated (second propellant is not burned) during activation of the first pulse. The ignition device for the second pulse (second ignition device) of this two-pulse rocket motor is required to have a function that initiates second propellant combustion and simultaneously rupturing the barrier membrane. Moreover, the second ignition device is required to ensure strength of the ignition device with respect to vibrations encountered during operation of the flying object and environmental factors such as heat during combustion of the first propellant without increasing structural weight by strengthening the structure in order to prevent a decrease in acceleration performance of the flying object.
However, in the case of the two-pulse rocket motor described in Patent Document 1, for example, a duplex structure, in which is placed a first ignition device and a second ignition device composed with an annular chamber around the front outer periphery thereof, is attached to the front end (end plate) of the rocket motor, and the structure of the attached portion is large in terms of both dimensions and weight.
In addition, in the case of placing a first ignition device and second ignition device in series as in the two-pulse rocket motor described in Patent Document 2, since the ignition devices have a long, narrow cantilever structure, it is necessary to strengthen the structure in order to ensure strength of the ignition devices with respect to environmental loads such as vibrations encountered during operation, thereby making this unsuitable for long motors due to the increase in structural weight.
In addition, in the barrier membranes and barrier membrane retaining structures of the two-pulse rocket motors described in Patent Document 1 and Patent Document 2, the rupturability and retainability of the barrier membrane during activation of the second ignition device are indistinct, and in the case the barrier membrane has been ruptured at an unexpected portion, combustion of the second propellant or flow of combustion gas is inhibited by the ruptured barrier membrane, or moreover it has the possibility of the nozzle choking by the ruptured barrier membrane depending on the particular case.
Patent Document 3 proposes a two-pulse rocket motor capable of solving the technical problems described in the aforementioned Patent Document 1 and Patent Document 2. The following provides an explanation of the two-pulse rocket motor described in Patent Document 3.
FIG. 1 is a longitudinal cross-sectional view showing an example of the two-pulse rocket motor described in Patent Document 3.
As shown in FIG. 1, a second ignition device 8 is protected from heat by a barrier membrane 10 in the same manner as a second propellant 5, and does not require protection from heat as a result of being burned out after activation.
A weak portion (joint) is provided in the barrier membrane 10 by employing a structure in which it is divided into two parts. More particularly, the barrier membrane 10 that covers the second propellant 5 is composed of a circular truncated conical aft barrier membrane 10a provided on the rear surface of the second propellant 10, and a cylindrical inner barrier membrane 10b provided on the inner peripheral surface of the second propellant 5. The end portion where the aft barrier membrane 10a and the inner barrier membrane 10b meet is joined with a fireproof adhesive over the entire circumference thereof to form a weak portion. This joint is not ruptured during combustion of the first propellant, but is reliably ruptured by operation of the second ignition device 8 or by gas generated by combustion of the second propellant 5.
During combustion of the second propellant 5, the inner barrier membrane 10b, which accounts for the majority of the barrier membrane 10, deforms towards the center and is maintained towards the front portion of the pressure vessel where flow generated by combustion gas of the second propellant 5 is comparatively gentle. In addition, the rupturing portion of the aft barrier membrane 10a deforms so as to be turned towards the rear along the flow of combustion gas. Thus, in addition to the aforementioned effects, the effect is obtained by which rupturability and retainability of the barrier membrane 10 (aft barrier membrane 10a and inner barrier membrane 10b) are distinct and definite.
In addition, the second ignition device 8 is provided close to the joint of the barrier membrane 10 (aft barrier membrane 10a and inner barrier membrane 10b) on the rear end of the second propellant 5, thereby further enhancing the reliability of rupturing of the barrier membrane 10 (aft barrier membrane 10a and inner barrier membrane 10b).
Furthermore, in the case of a two-pulse rocket motor of the form described above, since the second ignition device 8 has a structure that is isolated from a first ignition device 6 by the barrier membrane 10, the strength of the ignition devices can be ensured with respect to environmental factors such as vibrations encountered during operation without causing an increase in structural weight by strengthening the structure of the ignition devices even in the case of a long motor.